Sampling oscilloscopes are used to display repetitive waveforms of high frequency content greater than a few gigahertz. For non-repetitive, transient, isolated (single shot) waveforms, sampling oscilloscopes are limited to waveforms of relatively low frequency content (less than a gigahertz).
Electrically strobed sampling gates are commercially available. Analog/digital converters, diodes, and transistors are used at low frequencies in the kilohertz and megahertz region. In the gigahertz and higher frequency range, sampling oscilloscopes use balanced diode bridges on the 2,4 or 6 diode configurations. However, the dynamic range of the fast diode sampling gates is limited by the low reverse voltage breakdown of the diodes which can cause severe waveform distortion from electrical strobe feedthrough.
Commercially-available samplers can analyze repetitive waveforms with frequency contents of up to about 14 gigahertz. However, single-shot sampling devices have been limited to about 500 megahertz because of bandwidth limitations of the processing electronics, the analog switches, and the conversion rates of analog-to-digital converters.
Multiple sampling provides an alternative approach for single-shot sampling of non-repetitive waveforms. An array of electrically strobed switches spaced along a stripline can be activated simultaneously to take a picture of the waveform. For example, a multiple sampler using a series/parallel arrangement of 40 2-diode sampling gates spaced an equivalent of 45 picoseconds apart was shown to function over a bandwidth of about 3 gigahertz with multivolt sensitivity [Schwarte, R., "New Results of an Experimental Sampling System for Recording Fast Single Events", Electronic Letters, 8 (4), 94-96, February 24, 1972]. Among the difficulties with this system, was the accuracy of .+-.10 picoseconds required for the electrical pulse to each of 40 switches.
An optically strobed photoconductive sampling gate is one alternative to an electrically strobed diode gate that avoids the problems of electrical strobe feedthrough. For example, U.S. Pat. No. 4,030,840 of Lawton et al describes a waveform sampler using a gallium-arsenide photoconductor as the sampling gate and a conventional oscilloscope for display and to provide the strobe synchronization for repetitive pulses of light from a laser to sample a repetitive high-frequency waveform. The time resolution achievable with such a sampling device is limited by the duration of the optical impulses and the free-carrier lifetime of the photoconductor.
The above limitations related to photoconductor material or electrically strobed switches are avoided in the present invention based on electrooptic technology.
This invention is described in further complete detail in the dissertation entitled, "High Speed Integrated-Optic Sampler for Transient RF and Microwave Signals", by Richard William Ridgway (the applicant herein), submitted to the Graduate School of The Ohio State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy, December, 1985. This dissertation is incorporated herein by reference as fully as if it were presented in complete text.